PhD Student Tampere University Helsinki, Uusimaa, Finland
Background: Lower prenatal and childhood 25-hydroxyvitamin D (25(OH)D) concentrations have been linked with poorer neurocognitive abilities. However, there is a lack of randomized control trials (RCT) and studies using several 25(OH)D assessments across early life. Objective: To test if better neurocognitive abilities at 6-8 years are associated with (1) randomization to 1200IU or 400IU dose of vitamin D3 supplementation during first two years, (2) higher prenatal maternal and child's 12 and 24 months 25(OH)D levels and (3) 25(OH)D trajectories. Design/Methods: Participants were 296 children from Vitamin D intervention in infants (VIDI)-study. VIDI is a double-blind RCT in which healthy term-born children received either 400IU (n=135) or 1200IU (n=161) of vitamin D3 supplementation daily from age 2 weeks to 24 months. 25(OH)D levels were analyzed from blood serum collected from mothers at mean of 11.3 weeks of gestation, and from children at 12 and 24 months. Latent profile analysis (LPA) was used to model 25(OH)D trajectories across three measurements. Neurocognitive abilities were measured at 6.3-8.9 years. Total Intelligence quotient (IQ) score was assessed with Wechsler Intelligence Scale for Children (WISC-IV) (n=237), and executive functioning with NEPSY-II subtests (n=212) and parent-rated Behavior Rating Inventory of Executive Function (BRIEF-P) questionnaire (n=218). Linear regression analyses were used, and quadratic term was added to assess non-linear association. Results are presented after adjustment for sex. Other potential covariates i.e., maternal education, age, body-mass-index, or smoking, length of pregnancy, breastfeeding, or season of birth, were not associated with the outcome variables. Results: Neurocognitive abilities did not differ between intervention groups or according to the 25(OH)D levels at 12 or 24 months (all p-values>0.05). Maternal prenatal 25(OH)D levels were not associated with child’s executive functioning. However, a curvilinear association between maternal 25(OH)D levels and child’s total IQ score (quadratic estimate, p=0.01) was positive with lower 25(OH)D concentrations and negative with higher concentrations (vertex at 71.31 nmol/L). Two 25(OH)D trajectory groups estimated with LPA did not differ in their neurocognitive abilities.
Conclusion(s): We found no effect of infant vitamin D supplementation on neurocognitive abilities at age 6-8 years. However, both low and high prenatal maternal vitamin D concentrations were associated with lower IQ scores. Our results are preliminary and in need of replication.
